1. Field of the Invention
This invention relates to a tunnel driving method applied in NATM methods.
2. Prior Art
For tunnel driving and tunnel self-sustenance, NATM methods are conspicuous in these days.
As the NATM methods, there can be mentioned following methods.
(1) a full face cutting method
With this method, the full face of a tunnel is driven at once. Then, the method can be performed only when natural ground is stable.
(2) a long bench cut method
This method is performed when the length of a bench is generally longer than 50 m, natural ground is comparatively stable and invert closure should not be carried out so quickly. Further, this method includes two ways. One way is a simultaneous driving for the upper and lower portions of an inner section. Another way is an alternate driving for the upper and lower portions.
(3) a short bench cut method
This method is performed when the length of a bench is generally about from 15 to 30 m. This method is carried out with blasting treatment or mechanical treatment.
(4) a minibench cut method
This method is originally performed when invert closure should be carried out quickly due to unstable natural ground and/or the natural ground having large possibility of swelling. Actually, this method is seldom executed.
(5) a multistage bench cut method
If a tunnel has a comparatively large cross section, the facing of the tunnel can not self-sustain by normal bench cut methods. In this case, this multistage bench cut method can be used.
(6) a silot method
This method is performed when the face of a tunnel is comparatively large and natural ground does not have enough supporting strength against tunnel driving. Further, this method is often utilized in driving for town tunnels in order to prevent the settlement of the natural ground.
Next, from the view point of operation for driving a tunnel, the prior art will be explained. The conventional operation with drifters in the bench cut methods, particularly in the bench cut methods where the upper portion of the inner section is treated in prefer to the lower portion of the inner section, will be explained referring to FIG. 42. In the conventional operation, two drill carriages D, D are required. Each drill carriage D has two drill booms and one charging cage. The drill carriages D, D are placed on an upper stage U at its both sides with respect to the axis of a tunnel. First, blasting holes and rock bolt holes are marked with the charging cage. Next, as shown in FIG. (A), one rock bolt hole is bored with one drill boom of each drill carriage D. At the same time, one blasting hole of the upper portion is bored with another drill boom. Then, as shown in FIG. (B), rock bolts are inserted into the top and bottom of the upper portion with the charging cage while the drill carriages D, D are moved backward with a predetermined length. Subsequently, as shown in FIG. (C), the blasting holes are charged with the dynamite so as to blast the upper portion in order to make a new facing in the upper portion. As shown in FIG. (D), the two drill carriages D, D are moved backward to a lower stage L. Next, the same operation as the operation explained in FIGS. (A), (B) and (C) are carried out again also for the lower portion. Then, the above mentioned operation is started again and repeated several times. Mortar shooting is carried out with a mortar shooting apparatus having one arm. An air duct W is provided in the tunnel and a mortar injection car A is used for the mortar shooting so as to fix the rock bolts.
In the prior art, there are problems as follows.
(1) the full face cutting method
This method can not be used when the natural ground is unstable.
(2) the long bench cut method
As explained before, this method includes the two ways. First, in the simultaneous driving for the upper and lower portions, operation can be progressed in the both portions simultaneously without interval. Thus, it has an advantage that construction period is reliable. However, in the lower portion, many operators and apparatuses are required. Since priority is given to the operation in the upper portion, the operation in the lower portion can not be carried out efficiently. Accordingly, the construction cost of this method is expensive. Further, due to the simultaneous driving in the both portions, heavy machines and cars may be scraped each other, the operators may fall from a slope and muck from cars may hit the operators. Moreover, the work environment of this method is low. For example, when the lower portion is blasted, the air duct may be damaged resulting in incomplete ventilation. Further, blasting, mucking, concrete shooting are performed many times in the upper portion. Thus, dust is often produced in such operation. It is understood from the above description that the simultaneous driving has many problems.
On the other hand, in the alternate driving for the upper and lower portions, new facing is always formed in one portion; the upper portion or the lower portion. Accordingly, as for workability, safety and work environment, this alternate driving has advantages. Further, since the same apparatuses and operators can be used in the both portions, it can be carried out efficiently. However, when the natural ground is not unstable, it can not be performed smoothly, thus, its construction period can not be reliable. Further, in this alternate driving, it takes long time to remove and reset the air duct, electrical wires and the like.
(3) the short bench cut method
When this method is carried out with the blasting treatment, apparatuses should be prevented from being damaged by blasting operation. Accordingly, a slope must be formed so that the apparatuses can go up and down between the upper and lower portions through this slope. On the other hand, when this method is carried out with the mechanical treatment, it is very difficult to perform invert closure in short time.
(4) the minibench cut method
With this method, simultaneous operation in the upper and lower portions can not be performed actually, which means low workability.
(5) the multistage bench cut method
In this method, multiple stages are provided. Accordingly, closure is often carried out lately resulting in large deformation of a tunnel. Further, operation often disturbs each other.
(6) the silot method
In this method, generally, operation and invert closure can not be carried out in the both upper and lower portions at the same time. Accordingly, this method requires longer construction term and high construction cost.
Next, in the conventional operation with drifters, two drill carriages are used. Thus, machinery cost is increased and the number of operators are doubled. Further, there is a fear of scraping of the drill carriages on the both sides.
On the other hand, recently, many tunnels have large cross sections. In this situation, several number of drill carriages should be used effectively. However, actually, it is difficult to use the several number of drill carriages.